Online stopwatch

Laps, splits and totals

A lap (or split) is the time since the previous lap; the total is the time since you pressed Start. If you run four 400 m laps in 92, 90, 91 and 95 seconds, the total is 368 seconds (6:08) and the average lap is 92 seconds. Paste your laps into the mean calculator or the standard deviation calculator to see how consistent your pacing was: a low standard deviation means even laps.

Why time can drift on other stopwatches

Many web stopwatches add a fixed amount every timer tick, so they run slow when a tab is throttled. This one stores the start timestamp and computes now − start on every refresh, so a throttled tab only updates the display less often, never the result.

How to use the stopwatch

Press Start (or the space bar) to begin timing. Press Lap (or L) to record a lap without stopping the clock; each lap shows its own split time and the running total. Press Stop to pause and Start again to carry on from where you left off. Reset (or R when stopped) clears the time and all laps. On a computer, Full screen fills the display so a class, a gym or a team can read the time from across a room.

Reading the display

Time is shown as minutes, seconds and thousandths (mm:ss.mmm). Once it passes an hour, hours appear in front. The lap list shows, for each lap, the lap time (the split) and the cumulative time. The summary under the list gives the fastest lap, the slowest lap and the average lap, which helps you judge how steady your pacing was. Even laps mean even pacing; one slow lap stands out at once.

Accuracy

The stopwatch reads the browser clock at every refresh, so the time is accurate to a few milliseconds regardless of how busy the tab is. Your own reaction time is the bigger error: pressing a button typically adds 100 to 200 milliseconds at each end. For events that need hand timing to the hundredth of a second, use a dedicated timer and several people.

Good uses

• Timing running or swimming laps and comparing them with the pace calculator.
• Timing speeches, presentations and meeting contributions.
• Timing experiments in a science lesson, or recipe steps in the kitchen.
• Timing work tasks to estimate how long a job really takes.